1. Field of the invention
This invention relates to a biological agent and methods for inhibiting plant pathogens. More particularly, this invention relates to the use of Pseudomonas resinovorans (R. resinovorans) in the biological control of inter alia: Ralstonia solanacearum (R. solanacearum), Verticillium dahliae (V. dahliae) and Phytophthora infestans (P. infestans). This invention further relates to a biological combination agent for inhibiting Colletotrichum coccodes, in addition to the above pathogens.
For the purposes of this specification, a bacterium is deemed to be characterised by the bacterium deposited at the Centraalbureau voor Schimmelcultures under deposit number 100189, if there is a similarity of more than 85% between the other bacterium and the deposited bacterium, according to the BIOLOG identification system, of Biolog, Inc, 3938 Trust Way, Hayward, Calif. 94545, USA.
2. Description of the Prior Art
R. solanacearum (previously known as Pseudomonas solanacearum) is a soil-borne, pathogenic bacterium which causes bacterial wilt in plants and which is of substantial economic importance because it is endemic in most if not all the tropical and subtropical countries of the world. R. solanacearum colonises the roots of plants and penetrates the xylem and multiply within the vascular tissue of plants. Furthermore, it has a wide host range and the measures for controlling the disease are still limited.
Although some control measures for the biological control of R. solanacearum have been developed in vitro, a disadvantage of these measures is that they often fail in vivo and are seldom successful under natural conditions on a commercial scale. These biological control measures often fail under field conditions, because they are mainly based on the assumption that the biological agent is capable of competing with the pathogen under conditions that favour the pathogen, such as naturally infested soils. Reference is made, for example, to Trigalet, A., Frey, P. and Trigalet-Demery, D. 1994. Biological control of bacterial wilt caused by P. solanacearum: State of the art and understanding. In: Bacterial Wilt: The Disease and its causative agent, P. solanacearum (A. C. Hayward and G. L. Hartman, eds). CAB International pp. 225-233.
U.S. Pat. No. 4,663,162 discloses a method for inhibiting Verticillium wilt on a susceptible host plant, said method including the steps of applying to the host plant an effective amount of Bacillus polymyxa 9A, which has been designated A.T.C.C. accession number 39564.
A disadvantage of the said method disclosed in the above patent is that it is not effective against R. solanacearum. 
P. resinovorans has previously been isolated from maize root exudate. However, the antagonistic properties of P. resinovorans to R. solanacearum, V. Dahliae, and P. infestans have hitherto been unknown. The applicant has surprisingly found that P. resinovorans exhibits antagonistic properties to not only R. solanacearum, but also to V. dahliae and P. infestans and is able to compete with these pathogens in field conditions and on a commercial scale.
It is accordingly objects of the present invention to provide a biological agent and methods for the inhibition of plant pathogens, with which the aforesaid disadvantages may be overcome or at least minimised and to provide a useful alternative to the known agents and methods.
According to a first aspect of the invention there is provided a biological agent for inhibiting pathogens in susceptible plants and/or plant material including a bacterium characterised by a bacterium deposited at the Centraalbureau voor Schimmelcultures under deposit number 100189.
Further according to the invention the biological agent includes a bacterium that is of the strain deposited at the Centraalbureau voor Schimmelcultures under deposit number 100189.
Even further according to the invention the agent is effective in the biological control of any one or more of the pathogens selected from the group comprising Ralstonia solanacearum, Verticillium dahliae and Phytophthora infestans. 
The biological agent may include another antagonist to pathogens of Solanaceae plants.
The said other antagonist may comprise one or more antagonists selected from the group comprising Bacillus subtilis and Trichoderma harzianum. 
Preferably the other antagonist is non-pathogenic to plants of the family Solanaceae.
Further according to the invention the biological agent includes a carrier for the said bacterium.
The carrier may comprise particulate perlite.
The biological agent may further include a buffer and/or suitable nutrients for the said bacterium.
Preferably the ratio between the said bacterium and the carrier is in the range of between 1:8 to 1:12, on a mass per mass basis.
According to a second aspect of the invention there is provided a method for inhibiting pathogens in susceptible plants and/or plant material including the step of applying the above biological agent to such plants and/or plant material.
According to a third aspect of the invention there is provided a method for inhibiting pathogens in plants and/or plant material including the step of treating said plants and/or plant material with a bacterium characterised by a bacterium deposited at the Centraalbureau voor Schimmelcultures under deposit number 100189.
Further according to the invention the plants and/or plant material are treated with a bacterium that is of the strain deposited at the Centraalbureau voor Schimmelcultures under deposit number 100189.
Even further according to the invention the method is effective in the biological control of any one or more of the pathogens selected from the group comprising Ralstonia solanacearum, Verticillium dahliae and Phytophthora infestans. 
The method may include the further step of immobilising the said bacterium in a carrier comprising particulate perlite, a buffer, and nutrients.
The plant material may comprise a potato seed piece and the seed piece may be treated by applying the said bacterium as an aqueous suspension, prior to planting the seed piece. deposited at the Centraalbureau voor Schimmelcultures under deposit number 100189; and Bacillus subtilis. 
The biological combination agent may further include Trichoderma harzianum.